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theorem proved term proof

deLaValleePoussin_trig_kernel_eq_square

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formal statement (Lean)

  35theorem deLaValleePoussin_trig_kernel_eq_square (θ : ℝ) :
  36    3 + 4 * Real.cos θ + Real.cos (2 * θ) =
  37      2 * (Real.cos θ + 1) ^ 2 := by

proof body

Term-mode proof.

  38  rw [Real.cos_two_mul]
  39  ring
  40
  41/-- Positivity of the de la Vallee-Poussin trigonometric kernel. -/

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